1. Field of the Invention
The present invention relates to a controller and a control method for an internal combustion engine configured to control a flow rate of exhaust gas of an internal combustion engine which flows to a turbocharger, by operating an actuator to adjust an opening of a valve.
2. Description of the Related Art
A turbocharger has been installed in an internal combustion engine in order to, for instance, improve the output of an internal combustion engine (hereafter called “engine”). The turbocharger includes a turbine configured to rotate by the exhaust gas of the engine, and a compressor configured to operate by the rotation of the turbine.
In the case of operating such a turbocharger, the engine may be damaged when the engine is operated at high rotation and high load, and by the excessive rise of pressure in the intake passage of the engine, that is, the supercharging pressure. Therefore an exhaust bypass passage is disposed in parallel with the turbine of the turbocharger. Further, a part of the exhaust gas that flows in the exhaust passage is branched to the exhaust bypass passage using a waste gate valve disposed in the exhaust bypass passage, to adjust the flow rate of the exhaust gas to the turbine, and to control the supercharging pressure at an optimum value.
The waste gate valve opens/closes by the driving of a positive pressure actuator, for example. In concrete terms, the opening of the waste gate valve is adjusted by driving the positive pressure actuator when the pressure in the intake passage of the engine, particularly the pressure in the upstream portion of a throttle valve where pressure increases, becomes higher than the atmospheric pressure.
Normally in a period until the driving of the positive pressure actuator becomes possible, the waste gate valve is in a fully closed state. In the following description, the waste gate valve is called the WGV, and the waste gate actuator, which operates the WGV, is called the WGA.
In the case of the positive pressure actuator, the WGV cannot be operated unless the pressure in the intake passage of the engine becomes higher than the threshold. In other words, if this pressure is the threshold or less, the WGV cannot be operated, therefore the opening of the WGV cannot be changed.
As a result, recently a system that can freely restrict supercharging by the turbocharger by operating the WGA by electricity and driving the WGV when necessary, without depending on the pressure in the intake passage of the engine, was proposed. However, in this kind of system, an error is generated between the detected value of a WGV opening sensor and an actual WGV opening because of the influence of age related deterioration caused by the repeated opening/closing of the WGV for a long period of time, the temperature characteristics of the WGV opening sensor, the thermal expansion of the structure constituting the WGV and the like.
As a result, a reference position of the WGV, that is, a position of the WGV when the detected value of the WGV opening sensor is 0%, is shifted from the position where the WGV is the actual fully closed position. This means that even if the WGV is controlled to a target opening, the target opening is shifted from the actual WGV opening. As a consequence, control to a desired supercharging pressure may become impossible, or a supercharging pressure may not reach the control target value.
Therefore in a prior art according to Japanese Patent Application Laid-Open No. 2015-59549, if it is determined that the actual opening reached a fully closed state when the target opening is “fully closed”, the fully closed position is learned based on the output value of the opening sensor at this time, and the fully closed position learning value is corrected to a value that matches with the sensor output characteristic change, in accordance with the temperature change from the point when the fully closed position learning value was updated. By configuring [the controller] like this, the control accuracy of the WGV mechanism can be maintained, even if the temperature conditions change.